Iron(II) acetate is an organic metal compound which has been used for relatively long time and is a mordant used for black, dark gray or brown dyeing. At the present day, the iron(II) acetate is very importantly used in the fields of electronic industry and metal material industry as materials for magnetite and catalyst for fabricating carbon nanotube (CNT). High purity magnetite is prepared by thermolysis of the iron(II) acetate and used in various industrial fields such as magnetic fluid, magnetic resonance imaging (MRI), magnetic storage media, medical diagnosis, magnetically guided drug delivery, magnetic-field assisted cancer therapy, printing ink, oxidation of cyclohexane and catalyst for synthesizing ammonia (L. T. Chao et al., Journal of Physics: Conference Series, 26, 304-307 (2006); M. Klokkenburg et al., J. Am. Chem. Soc., 126, 16706-16707 (2004); S. Sun et al., J. Am. Chem. Soc., 124, 8204-8205 (2002); Y. Lee et al., Adv. Funct. Mater., 15(3), 503-509 (2005); R. Vijaya et al., Journal of Applied Physics, 89(11), 6324-6328 (2001); F. Z. Redl et al., J. Am. Chem. Soc., 126, 14583-14599 (2004); S. Music et al., Journal of Radioanalytical and Nuclear Chemistry, 121(1), 61-71 (1988); P. P. A. Filho et al., Reactivity of Solids, 3(3), 241-250 (1987); S. S. Jewur et al., Thermochimica Acta, 19(2), 195-200 (1977)); LIM sang-ho, Journal of the Korean Magnetics Society, 10(5), 256-267 (2000); S. S. Jewur et al., Thermochimica Acta, 19(2), 195-200 (1977); LEE Kyu-wan et al., Korean Patent No. 10-201871; J. Pinkas et al., Ultrasonics Sonochemistry (2007), doi:10.1016/j.ultsonch.2007.03.009; F. Montino et al., U.S. Pat. No. 5,221,657 (1993)).
The magnetite has half-metal properties due to high Curie temperature (860 K) and full spin-polarization. The half-metal, in which electrons of one spin orientation exhibit metal conductivity but electrons of the opposite orientation do not exhibit the metal conductivity, exhibits a giant magneto-resistance (GMR) in that an electrical resistance of a material is significantly changed when a magnetic field is applied, and plays a very important role as a spin electronic device. Since the magnetite exhibits tunneling magneto-resistance effect (a phenomenon in that a magneto-resistance is changed as a tunnel current between an insulator and a magnetic substance is changed by a magnetic field) which shows a magneto-resistance change rate of nearly 50% in the GMR, particularly at a room temperature, the magnetite enables high density recording and reading and is applied in a magnetic head for an ultra high density hard disk drive, a Magnetic Random access memory (MRAM) and a magnetic sensor.
The carbon nanotube was first discovered in 1991 and is used in various fields such as a field-effect transistor (FET), field emission arrays, storage of hydrogen and a fuel cell due to its unique physical-chemical properties of high strength, high elastic modulus, low frictional coefficient, chemical stability and electrical conductivity. As methods for preparing the carbon nanotube, chemical vapor deposition, catalytic pyrolysis, arc discharge and laser ablation are known. The iron(II) acetate is used as an organometallic catalyst which determines length, diameter, crystallinity and density of the carbon nanotube in the process for the preparation of the carbon nanotube by chemical vapor deposition(HAN In-tek, Korean Patent Laid open 10-2005-121426; HAN In-tek et al., Korean Patent Laid open 10-2006-2476).
In the process for the preparation of the iron(II) acetate suggested long time ago by Casey, Doyle and Montino, iron powder is dissolved in acetic acid in a nitrogen atmosphere and then stirred, thereby obtaining white (or light green) iron(II) acetate. When the iron(II) acetate solution is heated with oxygen addition, the iron(II) acetate is gradually changed into dark purple and black mixture and finally becomes orange colored basic Fe3(OH)2(CH3COO)72H2O as the acetic acid is vaporized (T. J. Kubik, Genome, 46, 527-528 (2003); R. S. Casey and J. R. Doyle, Kirk-Othmer encyclopedia of chemical technology, vol. 12, 2nd ed., Interscience, New York, 1967; F. Montino et al., U.S. Pat. No. 5,221,657). Also, Adams et al. prepared the iron(II) acetate by cathode oxidation using acetic anhydride together with ammonium acetate as an electrolyte (M. R. Adams et al., Transactions of the Kansas Academy of Science, 38, 129-130 (1935)).
With the cathode oxidation method or a method of dissolving the iron in the acetic acid, it is possible to recover high purity iron(II) acetate. These methods are however have a disadvantage that they cannot be employed in industrial applications. The known methods for the preparation of the iron(II) acetate are not preferred in consideration that i) most iron is produced in air or in the form of iron oxide (magnetite ore) and thus includes necessarily oxygen component, ii) it is possible to industrially mass produce the iron(II) acetate in general magnetite ore rather than in pure iron.
In order to improve the above problems, there have been made studies for preparing the iron(II) acetate from magnetite (Fe3O4 or Fe3O4.4H2O), hematite (α-Fe2O3), maghemite (γ-Fe2O3), goethite, (α-FeOOH), amorphous iron oxide hydrate (Fe3O4.xH2O) and limonite (FeO(OH).nH2O) which are produced in the form of a magnetite ore. Russian Patent No. 2,259,994 disclosed a process for the preparation of the iron(II) acetate from a mixture of acetic anhydride and aqueous acetic acid solution, iodine, hematite, magnetite, maghemite and Fe3O4. Reaction temperature is 80° C., reaction time is 2 hours and the yield is 72.8-99.9%. Also, Russian Patent Nos. 2,269,508 and 2,269,509 disclosed a process for the preparation of the iron(II) acetate from magnetite, iron(III) acetate and a mixture of acetic anhydride and aqueous acetic acid solution. Reaction temperature and reaction time are respectively 17° C.-25° C. and 1.8 hours, and the yield is 98.5%.
Accordingly, the present inventors found the possibility of the preparation of the iron(II) acetate from refined magnetite ore components from the Russian Patent documents and have been studying for preparing the iron(II) acetate from the magnetite ore including relatively low iron content in an economic process. As a result, the present inventors suggest a process for the preparation of high purity iron(II) acetate from low grade magnetites, which is simple, economic and mass producible.